Material for electric contacts taking silver-tin oxide or silver-zinc oxide as basis

ABSTRACT

The invention relates to a material for electric contacts taking silver tin-oxide as basis, consisting of silver or mainly silver-containing alloy, tin oxide and other oxides or carbides of tungsten, molybdenum, vanadium, bismuth, titanium, and/or copper.

BACKGROUND OF THE INVENTION

The invention relates to a material for electric contacts taking silvertin-oxide as basis, consisting of silver or a mainly silver-containingalloy, tin oxide and other oxides or carbides of tungsten, molybdenum,vanadium, bismuth, titanium, and/or copper. Such material is known frompatent WO 89/09478.

Because of their better environmental compatibility and their at leastpartly more favorable service life, the contact materials with silvertin oxide have begun to replace the previously preferred silvercadmium-oxide materials. However, because of its higher thermalproperties, tin-oxide's tendency under arcing effect to form poorlyconducting clinker layers on the surface, at constant current, thethermal behavior of silver tin-oxide contacts is unsatisfactory. Inorder to remedy this unsatisfactory property, to the generallypowder-metallurgically produced material are added powdered admixturesthat lead to a lower temperature at the contact points. As appropriateadmixtures, the patents disclose especially tungsten and molybdenumcompounds (DE-A-29 33 338, DE-A- 31 02 067, DE-A-32 32 627,EP-A-0024349). Bismuth and germanium compounds were further disclosed asadmixtures (DE-A-31 02 067 and DE-A-32 627). These admixtures help towet tin-oxide particles, so that the tin oxide remains finely divided insuspension when the contact piece surface melts under the effect of acontact arcing. Beside this positive effect in respect to the thermalbehavior under constant current, these admixtures have, however,undesirable secondary effects. The less than satisfactory plasticdeformation of the silver tin-oxide contact materials for theimprovement of which the tin-oxide powder is subject, by way of example,to a pre-treatment by calcining (DE-A-29 52 128), is further worsened bythe admixtures because of their embrittling effect. This appliesespecially to the bismuth and molybdenum oxides. Another disadvantage,particularly of the tungsten and molybdenum compounds, isthat--especially in switching operation under ACI stress (DIN 57660Section 102)--they contribute to a transfer of material, leading to anaccelerated burn-off and thus to a shortened service life.

As disclosed in WO 89/09478, a material for contacts presenting a lowwelding tendency and the lowest possible contact temperature can beobtained by purposefully producing a structure in which areas containinglittle or no metal oxide alternate with areas that contain the entiremetal oxide component, or the preponderant portion thereof, in minutedistribution. For this purpose, a composite powder is produced thatcontains the preponderant part of the tin oxide and the other oxidesand/or carbides, as well as a portion of the silver. This compositepowder is mixed, condensed, sintered, and transformed with the remainingsilver powder and eventually with the remaining part of the metaloxides. Although a suitable material is obtained in this manner, it isachieved by using a rather costly method.

The patent EP-A 0 369 283 discloses a sintered contact material forlow-voltage switch gears used in power engineering, in particular formotor contactors, the composition AgSnO₂ Bi₂ O₃ CuO. This composition isproduced by the internal oxidation of an AgSnBiCu alloyed powder that ismixed, compressed and sintered with a lesser amount of bismuth-zirconateand/or bismuth- titanate powder. This process reduces the strength ofthe AgSnO₂ Bi₂ O₃ CuO particles at the edge of the oxides, so thatbetween the particles is created a silver network that allows for highcompressed densities. However, both the manufacture of the alloy powderas well as its internal oxidation are costly and render the method quiteexpensive.

The object of this invention is to produce a material of the initiallystated type, that through the means of oxidic or carbidic admixturespresents a thermal behavior that is as advantageous as the knownmaterials for [electric] contacts without, however, being as brittle.

SUMMARY OF THE INVENTION

According to the invention, this object is solved by a materialpresenting the characteristics set forth in claims 1 or 2. Furtheradvantageous embodiments of the invention are the objects of thesubclaims.

The invention does not make the obvious attempt to find new admixturesthat lower the contact- point temperature without exercising or having alower embrittling effect. According to the invention, admixtures areused that are already known for this purpose and of which it is knownthat they have an embrittling effect. According to the invention,however, the chosen admixture is not used as a separate powder inaddition to silver powder and tin-oxide powder (DEoA-29 33 338, DE-A-3102 067, DE-A-32 6127) and also not as a component of a silver-tin oxidecomposite powder that is mixed with more silver powder and eventuallymetal oxide powders (WO 89/09478); rather, what is produced is amaterial containing tin-oxide areas in a matrix consisting of silver orof an alloy mainly consisting of silver, in which are concentrated theother oxides and/or carbides combined with the tin oxide and in whichthe silver matrix--apart from any possible soluble constituents - isfree of the other oxides and carbides. In these tin-oxide areas, theoxides can be present as single-phase mixed oxide or as a two-phase orpolyphase oxide mixture (e.g., in a particle compound or a laminarcompound). Such a material is preferably produced in apowder-metallurgically manner by mixing a silver powder or a silveralloy powder with a composite powder, in which the other oxides and/orcarbides are bound to the tin oxide; molded bodies are then extruded andsintered and, if necessary, redensified or reshaped. It is alsopossible, however, to mix the composite powder into a smelt of thematrix metal with subsequent solidifying.

Surprisingly, according to the invention, a certain decrease of thecontact point temperature under given operating conditions can alreadybe obtained with a lower percentage then previously of the chosen oxidicand/or carbidic admixture to the tin oxide, so that the contact materialis less brittle. Another advantage is that, because of the lowerpercentage of the electrically non-conductive admixture, the electricalresistance of the contact material is further reduced, which alsocontributes to a decrease of the contact point temperature.

Another advantage of the invention is that, because of the lowerpercentage of the chosen admixture, the service life of the contactpieces made out of the material is increased, because the admixtureswhich, such as molybdenum oxide, have the tendency to evaporate underthe influence of arcing, thanks to their lower percentage cause lessblistering leading thus to a lower burn-off.

Initial experiences with the contact material according to the inventionshow that a certain decrease of the contact point temperature, accordingto the invention, can be obtained even with only one fourth to one fifthof the amount of the admixed material which, according to thestate-of-the-art, would be necessary for the same decrease of thecontact point temperature.

Very little additional oxide or carbide, respectively, is needed if itis seen to it that these admixtures are concentrated in the boundaryarea of the tin-oxide areas to the silver matrix. Such a material can beobtained by mixing tin-oxide powder with the pulverized admixture andcalcining the mixture so that the tin-oxide powder particles are wettedby the admixture and/or a portion of the admixture diffuses into thesurface area of the tin-oxide particles, whereby a single-phase mixedoxide (e.g., a new chemical compound) or a two-phase or polyphase oxidemixture can be formed. For a longer service life of contact piecesaccording to the invention, it is advantageous if the additional oxidesand/or carbides are present not only in the boundary area of thetin-oxide areas to the silver matrix but also that the additional oxidesand/or carbides are present throughout the tin-oxide areas. Preferably,the tin-oxide composite powder is obtained by using a reaction-spraymethod, whereby a solution of tin salt and a salt of the metal or of themetals, of whose oxides or carbides the admixture shall consist, issprayed into a hot, oxidizing atmosphere, in which the salts arethermally disintegrated; thus, a finely divided composite powder isprecipitated, in which tin oxide and the oxides or mixed oxides of thealloy are present in a homogenous compound. The reaction-spray method isdisclosed, by way of example, in patents DE-C-29 630, U.S. Pat. No.3,510,291 and EP-A-0 012 202. A carbide-containing tin-oxide compositepowder can be obtained by suspending the carbide as a fine powder in thesolution to be sprayed. When the suspension is sprayed into a hot,oxidizing atmosphere, the tin oxide and the other oxides settle down onthe carbide particles, while the dwell time is held to a minimum so thatthe reducing effect of the carbide does not exert any influence.

The reaction-spray method can also be advantageously used to obtain atin-oxide powder, of which the surface is coated with the other oxides,by suspending, as a variation of the above-described method, a finelydivided tin-oxide powder in the saline solution instead of the tin salt,and by spraying this suspension into a hot, oxidizing atmosphere.

Finally, it is also possible to suspend in a solution a part of theoxides, to which tin oxide can also belong, and eventually also carbidesthat shall be contained in the material as admixture; this solutioncontains the metals for the remaining oxide component of the materialand the thus formed solution is sprayed according to reaction-spraymethod. In such a manner it is possible to produce composite powderswith a variety of modified structures, adapted for the specificapplication of the contact material.

In order to guarantee the assurance against a fusing of the contactpieces that is required from the silver-metal oxide materials, thematerial contains advantageously 5 to 20 weight per cent, preferably 8to 15 weight per cent of tin oxide; in order to maintain the tin oxidethrough the admixtures in suspension in the molten phase occurring underarcing effect, the tin-oxide powder should contain 0.01 to 10 weight percent of the other oxidic or carbidic admixture, advantageously, however,not more than 5 weight per cent. In view of the fact that the materialshall be as least brittle as possible, the admixture of the other oxidesand carbides is chosen as low as possible, so as not to exceed acontact-point temperature given under the predetermined conditions ofapplication, for which suffice considerably lower amounts than for thestate-of-the art. Preferably, a tin-oxide powder is used that containsonly 0. 1 to 1.5 weight per cent of the other oxide or carbide.

The tin-oxide areas in the material are advantageously smaller than 100μm, preferably smaller than 10 μm in diameter, but they should not besmaller than 0.5 μm so as not to cause any dispersion strengthening.

An especially preferred admixture is molybdenum because of itsparticularly advantageous effect on the thermal behavior.

The patent's theory can be applied to contact materials taking silverwith zinc oxide as basis. Currently there are practically no admixt isattempted to obtain a decrease of the contact-point temperatures bymeans of structural measures. By using a tin oxide enriched with otheroxides and/or carbides, according to the invention, it is possible toobtain a decrease of the contact-point temperature for this material aswell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results of a temperature rise test of an embodiment ofthe invention.

FIG. 2 shows the results of a temperature rise test of the prior art.

FIG. 3 shows a comparison of the total burn-off of contact pieces as afunction of the number of switching cycles for the invention and theprior art.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLES Example 1

A tin oxide-molybdenum oxide composite powder with 1 weight per centmolybdenum oxide is produced by spraying an aqueous solution oftin(II)-chloride and molybdenum(IV)-chloride into a reactor with anoxidizing atmosphere, heated to about 950° C.; this process yields a tinoxide- molybdenum oxide composite powder, in whose powder particles arepresent very finely divided tin oxide and molybdenum oxide.

12 weight per cent parts of the thus produced tin-oxide powder, dopedwith molybdenum oxide, are thoroughly mixed with 88 weight per centparts of a silver powder with a particle size of less than 40 μm; fromthe mixture is isostatically cold-pressed a cylindrical block weighing50 kg, that is sintered in air and held for 1/2 hours at a temperatureof 820° C. The sintered block is encased in silver, placed hot into areverse extrusion press and extruded by an extrusion die through abranched extrusion aperture; thus are produced two flat strands thatpresent on one side a silver-tin oxide surface and on the other side areadily solderable and weldable silver surface. Subsequently, thestrands are rolled flat and are then 8 cm wide and 2 mm thick.

Example 2

The first example is modified to the effect that, instead of solutionconsisting of tin(II)-chloride and molybdenum(IV)-chloride, amolybdenum(IV)-chloride solution is sprayed, in which is suspended atin-oxide powder having a particle size of less than 5 μm.

Contact pieces produced according to example 1 present an increase ofthe contact point temperature only after a rather large number ofswitching operations. Presumably, this is connected with the otherstructure of the tin oxide-molybdenum oxide composite powder, andpossibly also with the forming of a mixed oxide.

Example 3

A tin alloy with 2 weight per cent of copper as well as 1 weight percent of bismuth is heated to a temperature of 580° C. and sprayed bymeans of a two-component nozzle into a reactor with oxygenousatmosphere, that is at room temperature. According to Fisher, thus isproduced a mixed oxide powder with a particle diameter of 4.5 μm. 10weight per cent of this mixed oxide powder are mixed with a silverpowder having a particle diameter of less than 40 μm; from the mixture acylindrical block is isostatically cold-pressed at a pressure of 7,85.10n/m², that is sintered in air for 2 hours at a temperature of 790° C.,and subsequently extruded with an extruder, forming a wire with adiameter of 5 mm. By drawing, this wire is tapered down to a diameter of1.4 mm and subsequently machined to form contact rivets; the diameter oftheir top is 3.2 mm while the diameter of the shank is 1.47 mm. Beinginstalled in a relay, the new material proved to be markedly superior tothe contact materials corresponding to the state-of-the-art whensubjected both to the A.C. service life test and the switching of theD.C. lamp load.

Example 4

From an aqueous solution of tin chloride and meta-tungstic acid isproduced a mixed oxide powder by spraying the solution into a reactorthat is heated to 1100° C. The tin-tungsten oxide mixture obtained insuch a manner has a percentage of tungsten oxide of 1 weight per cent,and a mean particle diameter of 2.4 μm.

As in example 1, the oxide powder is mixed with silver powder andmachined to form contact lamellas.

Example 5

An aqueous solution of tin acetate and ammonium heptamolybdate issprayed into a reactor at a temperature of 800° C.; thus is obtained anoxide powder with a molybdenum content of 350 ppm and a mean particlediameter of 1.9 μm. As in example 1, from this powder is produced acontact material that is subjected to a service life test according totest category AC1 in a switchgear having a power of 37 kW. This servicelife test is interrupted in order to carry out a temperature-rise testwith constant current supply.

FIG. 1 shows the result of this temperature-rise test and it is comparedwith an analogous test of a material corresponding to thestate-of-the-art consisting of 88 weight per cent Ag, 11.6 weight percent SnO₂ and 0.4 weight per cent of MoO₃ (FIG. 2).

It can be seen that the thermal behavior of the new material is as goodas that of the conventional material although the new material, asregards the entire contact material, presents a molybdenum oxidepercentage of merely 42 ppm while, for the same advantageous result, thematerial corresponding to the state-of-the-art requires a molybdenumpercentage of 0.4 weight per cent, i.e., approximately one hundred timesas much.

Example 6

An aqueous solution of tin chloride, bismuth oxide and copper chlorideis sprayed into a reactor with a temperature of 1200° C., and a mixedoxide powder having a bismuth oxide content of 0.8 weight per cent and acopper oxide content of 1.5 weight per cent, as well as mean particlesize of 3 μm, is obtained. As in example 1, contact lamellas areproduced from this product. In this connection, it can be seen that thenew contact material, in contrast to those that are produced by thecustomary powder-metallurgical method and contain bismuth oxide, isreadily deformable. The obtained contact lamellas are subjected to aservice life test in a motor contactor according to test category AC3.FIG. 3 shows the total burn-off of the contact pieces as a function ofthe number of switching cycles for the new material as well as for theone corresponding to the state-of-the-art. As it can be seen, thematerial consumption of the new material is much less than that of thecustomary material, a fact that results in an increase of the electricalservice life by approximately 50%. It is difficult to produce contactlamellas out of silver-tin oxide-copper oxide-bismuth oxide according tothe conventional powder-metallurgical methods, because the embrittlingeffect of the bismuth oxide leads to fissures when deforming the contactmaterial.

What is claimed is:
 1. All electrical contact material comprising:ametal component as a major ingredient; and the remainder being a mealoxide component as a minor ingredient, said metal component present inthe form of a silver matrix, and said metal oxide component present inthe form of the oxide particles and one of an other metal oxide/carbideparticles selected from the group consisting of molybdenum, tungsten,antimony, germanium, vanadium, and indium, said other carbides/oxidescomprising up to 40 percent of a weight percentage of said tin oxide insaid material, wherein said silver matrix includes areas of tin oxideand is free of said other oxide/carbide particles, said otheroxide/carbide particles confined in a boundary area between saidtin-oxide particles and said silver matrix.
 2. The electrical contactmaterial of claim 1, wherein said other oxide/carbide particles are alsocontained within said tin-oxide areas as a homogeneous compound of saidtin-oxide and other oxide/carbide particles.
 3. The electrical contactmaterial of claim 1 wherein a total fraction of the tin oxide and of theother oxides/carbides amounts to 8 to 20 weight percent of a totalweight of the material.
 4. The electrical contact material of claim 3,wherein the total fraction of the tin oxide and of the otheroxides/carbides amounts to 8 to 15 weight per cent of the total weightof the material.
 5. The electrical contact material according to claim 1wherein the tin-oxide areas are comprised of at least 0.01 weight percent of the other oxides/carbides.
 6. The electrical contact materialaccording to claim 1 wherein the tin-oxide areas contain up to 10 weightper cent of the other oxides/carbides.
 7. The electrical contactmaterial of claim 1, wherein the tin-oxide areas contain up to 5 weightper cent of the other oxides/carbides.
 8. The electrical contactmaterial of claim 1, wherein the tin-oxide areas contain up to 2.5weight per cent of the other oxides/carbides.
 9. A material according toclaim 5, characterized by the fact that the tin-oxide areas contain 0.1to 1.5 weight per cent of the other oxides and/or carbides.
 10. Theelectrical contact material of claim 1 wherein the homogeneous mixtureis obtained by a calcining of a mixture of said tin oxide and otheroxide/carbide particles such that said tin oxide particles are wetted bysaid mixtures such that a portion of said mixture diffuses into thetin-oxide powder particles end produces one of a single and a dual mixedphase oxide compound.
 11. The electrical contact material of claim 2,wherein the homogeneous mixture is obtained by spraying a solution of atin salt, a salt of the metal component, and one of said otheroxides/carbides into a hot, oxidizing atmosphere in which the salts arethermally disintegrated, resulting in a precipitation of a finelydivided composite powder, the composite powder presenting a homogeneouscompound of mixed oxides.
 12. The electrical contact material of claim1, wherein said carbide particles are covered with the tin oxide and theother oxides.
 13. The electrical contact material of claim 11, wherein acarbide-containing tin-oxide homogeneous mixture can be obtained bysuspending the carbide as a fine powder in the solution to be sprayed.14. The electrical contact material to claim 1 that is obtained byspraying into a hot, oxidizing atmosphere a suspension of tin oxide saidother oxides/carbides that the material shall contain in addition to thetin oxide, in a solution of a salt of the metal, the oxides of whichshall be contained in the material as a residual, oxidizing componentwherein the salts are thermally converted into oxides and settle ontoone of the oxide particles and carbide particles stemming from thesuspension.
 15. The electrical contact material according to claim 1wherein the tin-oxide areas have a diameter of less than 100 μm.
 16. Amaterial according to claim 15, wherein the tin-oxide areas have adiameter of not more than 10 μm.
 17. A material according to claim 1wherein the tin-oxide areas have a diameter of at least 0.5 μm.
 18. Amaterial according to claim 1 wherein the tin is replaced with zinc. 19.An electrical contact material comprising:a metal component as a majoringredient; and the remainder being a metal oxide component as a minoringredient, said metal component present in the form of a silver matrix,and said metal oxide component present in the form of a combination oftin oxide and zinc oxide particles and one of an other metaloxide/carbide particles selected from the group consisting ofmolybdenum, tungsten, antimony, germanium, vanadium, and indium, saidother carbides/oxides comprising up to 40 percent of a weight percentageof said combination of tin oxide and zinc oxide in said material,wherein said silver matrix includes areas of a combination of tin oxideand zinc oxide and is free of said other oxide/carbide particles, saidother oxide/carbide particles contained in a boundary area between saidcombination of tin oxide and zinc oxide particles and said silvermatrix.
 20. The electrical contact material of claim 19 wherein a totalfraction of the combination of tin oxide and zinc oxide and of the otheroxides/carbides amounts to 8 to 20 weight percent of a total weight ofthe material.
 21. The electrical contact material of claim 20, whereinthe total fraction of the combination of tin oxide and zinc oxide and ofthe other oxides/carbides amounts to 8 to 15 weight per cent of thetotal weight of the material.
 22. The electrical contact materialaccording to claim 19 wherein the combination of tin oxide and zincoxide areas are comprised of at least 0.01 weight per cent of the otheroxides/carbides.
 23. The electrical contact material according to claim19 wherein the combination of tin oxide and zinc oxide areas contain upto 10 weight per cent of the other oxides/carbides.
 24. The electricalcontact material of claim 19, wherein the combination of tin oxide andzinc oxide areas contain up to 5 weight per cent of the otheroxides/carbides.
 25. The electrical contact material of claim 19,wherein the combination of tin oxide and zinc oxide areas contain up to2.5 weight per cent of the other oxides/carbides.
 26. The electricalcontact material of claim 19 wherein the homogeneous mixture is obtainedby a calcining of a mixture of said combination of tin oxide and zincoxide and other oxide/carbide particles such that said combination oftin oxide and zinc oxide particles are wetted by said mixtures such thata portion of said mixture diffuses into the combination of tin oxide andzinc oxide powder particles end produces one of a single and a dualmixed phase oxide compound.
 27. The electrical contact material of claim19, wherein the homogeneous mixture is obtained by spraying a solutionof a tin salt, a salt of the metal component, and one of said otheroxides/carbides into a hot, oxidizing atmosphere in which the salts arethermally disintegrated, resulting in a precipitation of a finelydivided composite powder, the composite powder presenting a homogeneouscompound of mixed oxides.
 28. The electrical contact material of claim19 wherein said carbide particles are covered with the combination oftin oxide and zinc oxide and the other oxides.
 29. The electricalcontact material of claim 19, wherein a carbide-containing a combinationof tin oxide and zinc oxide homogeneous mixture can be obtained bysuspending the earbide as a fine powder in the solution to be sprayed.30. The electrical contact material to claim 19 that is obtained byspraying into a hot, oxidizing atmosphere a suspension of a combinationof tin oxide and zinc oxide said other oxides/carbides that the materialshall contain in addition to the combination of tin oxide and zincoxide, in a solution of a salt of the metal the oxides of which shall becontained in the material as a residual, oxidizing component wherein thesalts are thermally converted into oxides and settle onto one of theoxide particles and carbide particles stemming from the suspension. 31.The electrical contact material according to claim 21 wherein thecombination of tin oxide and zinc oxide areas have a diameter of lessthan 100 μm.
 32. A material according to claim 31, wherein thecombination of tin oxide and zinc oxide areas have a diameter of notmore than 10 μm.
 33. A material according to claim 19 wherein thecombination of tin oxide and zinc oxide areas have a diameter of atleast 0.5 μm.
 34. A material according to claim 19 wherein the tin isreplaced with zinc.
 35. An electrical contact material comprising:ametal component as a major ingredient; and the remainder being a metaloxide component as a minor ingredient, said metal component present inthe form of a silver matxix, and said metal oxide component present inthe form of zinc oxide particles and one of an other metal oxide/carbideparticles selected from the group consisting of molybdenum, tungsten,antimony, germanium, vanadium, and indium, said other carbides/oxidescomprising up to 40 percent of a weight percentage of said zinc oxide insaid material, wherein said silver matrix includes areas of zinc oxideand is free of said other oxide/carbide particles, said otheroxide/carbide particles contained in a boundary area between saidzinc-oxide particles and said silver matrix.
 36. The electrical contactmaterial of claim 35 wherein a total fraction of the zinc oxide and ofthe other oxides/carbides amounts to 8 to 20 weight percent of a totalweight of the material.
 37. The electrical contact material of claim 36,wherein the total fraction of the zinc oxide and of the otheroxides/carbides amounts to 8 to 15 weight per cent of the total weightof the material.
 38. The electrical contact material according to claim35 wherein the zinc oxide areas are comprised of at least 0.01 weightper cent of the other oxides/carbides.
 39. The electrical contactmaterial according to claim 35 wherein the zinc oxide areas contain upto 10 weight per cent of the other oxides/carbides.
 40. The electricalcontact material of claim 35, wherein the zinc oxide areas contain up to5 weight per cent of the other oxides/carbides.
 41. The electricalcontact material of claim 35, wherein the zinc oxide areas contain up to2.5 weight per cent of the other oxides/carbides.
 42. The electricalcontact material of claim 35 wherein the homogeneous mixture is obtainedby a calcining of a mixture of said zinc oxide and other oxide/carbideparticles such that said zinc oxide particles are wetted by saidmixtures such that a portion of said mixture diffuses into the zincoxide powder particles end produces one of a single and a dual mixedphase oxide compound.
 43. The electrical contact material of claim 35,wherein the homogeneous mixture is obtained by spraying a solution of atin salt, a salt of the metal component, and one of said otheroxides/carbides into a hot, oxidizing atmosphere in which the salts arethermally disintegrated, resulting in a precipitation of a finelydivided composite powder, the composite powder presenting a homogeneouscompound of mixed oxides.
 44. The electrical contact material of claim35, wherein said carbide particles are covered with the zinc oxide andthe other oxide.
 45. The electrical contact material of claim 35,wherein a carbide-containing zinc oxide homogeneous mixture can beobtained by suspending the carbide as a fine powder in the solution tobe sprayed.
 46. The electrical contact material to claim 35 that isobtained by spraying into a hot, oxidizing atmosphere a suspension ofzinc oxide said other oxides/carbides that the material shall contain inaddition to the zinc oxide, in a solution of a salt of the metal theoxides of which shall be contained in the material as a residual,oxidizing component wherein the salts are thermally converted intooxides and settle onto one of the oxide particles and carbide particlesstemming from the suspension.
 47. The electrical contact materialaccording to claim 35 wherein the zinc oxide areas have a diameter ofless than 100 μm.
 48. A material according to claim 47, wherein the zincoxide areas have a diameter of not more than 10 μm.
 49. A materialaccording to claim 35 wherein the zinc oxide areas have a diameter of atleast 0.5 μm.
 50. A material according to claim 35 wherein the tin isreplaced with zinc.